RAPHEX EVALUATION TEST QUESTIONS AND
ANSWERS SURE A+
✔✔As the size of the active volume of the ionization chamber increases, the amount of
charge generated for a given dose
A. increases
B. decreases
C. remains the same
D. cannot be determined - ✔✔A. increases. PV= nRT!
✔✔Which of the following is particularly important to consider when using an ion
chamber for a flattening-filter-free photon beam measurement compared to
measurement of a flattened beam?
A. temperature and pressure
B. polarity correction
C. stem effect
D. leakage current
E. ion recombination - ✔✔E. ion recombination
✔✔The charge measured by an ionization chamber is ______ the pressure of the gas in
the chamber.
A. unrelated to
B. directly proportional to
C. inversely proportional to
D. proportional to the square of
E. proportional to the inverse square of - ✔✔B. directly proportional to. PV=nRT!
✔✔If the raw transmission values for radiochromic films exposed to 0 Gy and 250 Gy
are 30,000 and 3000, respectively, what is the net optical density corresponding to 250
cGy?
A. 10.0
B. 4.5
C. 3.5
, D. 2.4
E. 1.0 - ✔✔E. 1.0. The optical density is a measure of the amount of light that can pass
through exposed film, which can be related to the dose received by the film. The optical
density is defined as OD =log (lo/I) where lo and I, are the transmission values
measured before and after an exposure, respectively.
✔✔A patient is being treated AP/PA isocentrically with 6-MV x-rays. The actual patient
separation is 1 cm smaller than the separation used for the MU calc. What is the
approximate dose error to midplane depth?
A. There is no error.
B. 1.5%
C. 5%
D. 7.5%
E. 10% - ✔✔B. A rule of thumb for photon attenuation is about 3%/cm for 6-MV photons
in tissue. Decreasing the separation with the same MU will result in an overdose.
✔✔Beam quality, as measured by %dd(10) of flattened beams, is approximately
________________ compared to flattening-filter-free (FFF) beams.
A. 20% higher
B. 5% higher
C. the same
D. 5% lower
E. 20% lower - ✔✔B. Flattened beams are slightly harder than flattening-filter-free
beams due to beam hardening in
the flattening filter.
✔✔Machine "A" is calibrated to give 1 Gy/MU at dmax with a source-to-surface distance
of 100 cm SSD. Machine "B" is calibrated to give 1 cGy/MU at 10 cm depth at 100 cm
SSD. For the same MU ______delivers a greater dose at dmax•
A. machine "A"
B. machine "B"
C. Both deliver the same dose.
D. There is not enough information to answer this question. - ✔✔B. Machine "B" will
generate approximately 1/PDD(@ 10) more dose at dmax than Machine "A" per
MU. MU is not an absolute dose quantity. It is related to the dose delivered to a
calibration
point, so if two machines are calibrated at different points, the dose per MU at dmax will
also
differ.
✔✔A 10X10 cm^2 6-MV photon field is incident upon a flat phantom. On the plane
perpendicular to the beam central axis at max, the dose to a point 1cm outside of the
edge of the collimated field is of the order of ____% of the field maximum dose.
A. 0.05%
B. 0.5%
ANSWERS SURE A+
✔✔As the size of the active volume of the ionization chamber increases, the amount of
charge generated for a given dose
A. increases
B. decreases
C. remains the same
D. cannot be determined - ✔✔A. increases. PV= nRT!
✔✔Which of the following is particularly important to consider when using an ion
chamber for a flattening-filter-free photon beam measurement compared to
measurement of a flattened beam?
A. temperature and pressure
B. polarity correction
C. stem effect
D. leakage current
E. ion recombination - ✔✔E. ion recombination
✔✔The charge measured by an ionization chamber is ______ the pressure of the gas in
the chamber.
A. unrelated to
B. directly proportional to
C. inversely proportional to
D. proportional to the square of
E. proportional to the inverse square of - ✔✔B. directly proportional to. PV=nRT!
✔✔If the raw transmission values for radiochromic films exposed to 0 Gy and 250 Gy
are 30,000 and 3000, respectively, what is the net optical density corresponding to 250
cGy?
A. 10.0
B. 4.5
C. 3.5
, D. 2.4
E. 1.0 - ✔✔E. 1.0. The optical density is a measure of the amount of light that can pass
through exposed film, which can be related to the dose received by the film. The optical
density is defined as OD =log (lo/I) where lo and I, are the transmission values
measured before and after an exposure, respectively.
✔✔A patient is being treated AP/PA isocentrically with 6-MV x-rays. The actual patient
separation is 1 cm smaller than the separation used for the MU calc. What is the
approximate dose error to midplane depth?
A. There is no error.
B. 1.5%
C. 5%
D. 7.5%
E. 10% - ✔✔B. A rule of thumb for photon attenuation is about 3%/cm for 6-MV photons
in tissue. Decreasing the separation with the same MU will result in an overdose.
✔✔Beam quality, as measured by %dd(10) of flattened beams, is approximately
________________ compared to flattening-filter-free (FFF) beams.
A. 20% higher
B. 5% higher
C. the same
D. 5% lower
E. 20% lower - ✔✔B. Flattened beams are slightly harder than flattening-filter-free
beams due to beam hardening in
the flattening filter.
✔✔Machine "A" is calibrated to give 1 Gy/MU at dmax with a source-to-surface distance
of 100 cm SSD. Machine "B" is calibrated to give 1 cGy/MU at 10 cm depth at 100 cm
SSD. For the same MU ______delivers a greater dose at dmax•
A. machine "A"
B. machine "B"
C. Both deliver the same dose.
D. There is not enough information to answer this question. - ✔✔B. Machine "B" will
generate approximately 1/PDD(@ 10) more dose at dmax than Machine "A" per
MU. MU is not an absolute dose quantity. It is related to the dose delivered to a
calibration
point, so if two machines are calibrated at different points, the dose per MU at dmax will
also
differ.
✔✔A 10X10 cm^2 6-MV photon field is incident upon a flat phantom. On the plane
perpendicular to the beam central axis at max, the dose to a point 1cm outside of the
edge of the collimated field is of the order of ____% of the field maximum dose.
A. 0.05%
B. 0.5%
